This invention relates to a method of determining the molecular weight distribution of carboxymethylcellulose or a salt thereof (hereinafter referred to briefly as CMC).
While CMC is conventionally produced from pulp, an efficient quality and process control through its manufacturing stage demands that the conditions of molecular weight distribution analysis of CMC be identical with those of the material pulp.
The molecular weight is generally determined by gel permeation chromatography (hereinafter referred to briefly as GPC).
In the conventional GPC technology for molecular weight distribution analysis, said two determinations (for pulp and CMC) cannot be carried out under identical conditions because pulp and CMC cannot be dissolved within the same time period, the necessary derivatization of pulp complicates the determination procedure and/or the aging of the column packing is rapid and severe, to mention Just a few difficulties.
For these reasons, GPC analyses of the molecular weight distributions of pulp and CMC have heretofore been performed using different mobile phase solvents under different conditions, thus presenting the problem that the molecular weight distribution of starting pulp and that of CMC cannot be exactly compared in equal terms.
The conventional GPC determination of starting pulp involves the use of a cascade of 2-3 columns packed with hydrous materials and, as the mobile phase solvent, many solvent species such as an aqueous solution of iron sodium tartrate complex, an aqueous solution of cadoxen, etc. in the case of aqueous systems or paraformaldehyde-dimethyl sulfoxide, etc. in the case of non-aqueous systems.
Incidentally, Graham Agg and coworkers reported in 1980 that they determined the molecular weight distributions of sulfite pulp and PHK pulp by GPC using an aqueous solution of iron sodium tartrate complex as the mobile phase solvent but their samples for analysis were pulps and not CMC (Int. Dissolving Pulps Conf. [Conf. Pap.] 5th, 224-229. TAPPI).
Meanwhile, the GPC analysis of CMC has been performed using 3-4 columns packed with hydrous materials and, as the mobile phase solvent, aqueous solutions of sodium chloride, sodium nitrate, etc.